A variety of prosthetic foot designs have been developed in recent, years to give more versatility to the user. Traditionally, prosthetic feet were constructed with relatively solid or rigid ankle blocks augmented by some for of elastic or flexible cushioning in the heal area such as often provided by a low density elastomeric foam under the solid ankle. This type of early prosthetic foot construction is known as the SACH foot as an acronym for "solid ankle cushion heel". The construction and functioning of the SACH foot offered comforting stability when the user is standing but did little to assist the user in walking, or moderate to athletic running and jumping. This early prosthetic foot standard had the feel of a "dead" foot lacking a natural quality of rebound or spring back and/or forward thrust to assist the gait of the wearer.
To improve upon the dynamic performance of the SACH foot, innovative foot designs offered various forms of energy storage in one or more various configurations of spring keels. Thus, more recent prosthetic feet with energy storage enabled natural interaction between the cyclic loading and unloading of the foot during body movement to more closely simulate the natural foot leg body gait. Examples of these recent dynamic response energy storage feet are found in U.S. Pat. Nos. 4,547,913 and 5,066,305. While the energy storage prosthetic foot has enjoyed great acceptance and increased the athletic range of users, there still remains a need for a less dynamic foot prosthesis; one that offers particular comfort in walking providing rollover ease and some energy storage and return to make the foot more lively than the traditional SACH's foot design.
In this regard, a dynamic response keel designed for the very active and athletic user exhibits a somewhat stiff feel and the user may have the uncomfortable sensation of vaulting over a stiff toe, i.e., difficulty in following through with forward rotation as the gait progresses to and through lift off. This is because the foot must rotate over the relatively stiff keel tip of the dynamic response keel compared to the older SACH foot.
Thus, it is an aspect of the present invention to provide an improvement over known prosthetic feet by providing greater stationary stability and more comfortable rollover feel especially during walking in a light to moderate energy storage and energy return foot so as to give a livelier sensation compared to the traditional SACH's foot. Another aspect in to provide an improved prosthetic foot with sharply progressive stiffening so as to not give way under occasional heavy load.
It is a further aspect of the present invention to provide an improved foot prosthesis having a structural design that accommodates a wide range of customizable stiffness, using the same basic keel configuration.
Still another aspect of the invention is to provide a keel design and prosthetic foot having the above improvements and configured in a geometry that is capable of being mass manufactured into a light weight product at a relatively low per unit cost by injection molding the keel as a unitary structure made up of thin walls.